Bulgarians like to have holidays, they have a rich history and hence - a lot of official feasts - non-working days.
January 1st - New Year's Day
March 3rd - Liberation Day
April 24th - Easter (not in the same date every year)
May 1st - Labour Day
May 6th - St. George's Day - The Feast of the Bulgarian Army, and Name Day of a lot of Bulgarians. (In Bulgaria we use to celebrate on a particular date the name of someone - let's say - St. George - and on that day everybody who's name is George celebrate. This is something like a birthday, but connected to your name. The saying is that you can go to someone's name day even without invitation.)
May 24th - Saints Cyril & Methodius - these are the people who invented the Cyrillic alphabet that we - Bulgarians use. Every year, on this date we honour them by celebrating the Day of Bulgarian Culture and Slavonic Letters..
September 6th - Unification Day - celebrating the Union of Bulgaria and Eastern Rumelia in 1885.
September 22nd - Independence Day
December 24, 25, 26th - Chirstmas.
December 31st - New Year's Eve.
So - Bulgarian people has about 10 days of the year for official holidays. And this, combined with the above mentioned Name days and Birthdays explains why there are so many people celebrating from the early night to the early hours of the next day, gathering around the family table, with home made delicious food.